Waste treatment plant and process

ABSTRACT

A waste treatment process including the steps of: (i) passing waste material which may comprise animal or human faeces comprising an insoluble component such as lignocellulose through a bioreactor system including a plurality of bioreactors in series and maintaining said insoluble component as a suspension in said waste material; and (ii) separating suitably by filtration the insoluble component from the waste material. A waste treatment plant including: (i) a bioreactor system including a plurality of bioreactors in series for treatment of waste material; (ii) means such as filtration for separating an insoluble component from said waste material after passage through the bioreactor system.

FIELD OF THE INVENTION

THIS INVENTION relates to a waste treatment plant and process.

BACKGROUND ART

Hitherto disposal of waste including faeces from livestock feedlotsincluding piggeries, beef cattle feedlots, dairy cattle milking shedsand holding yards, and poultry farms which were operated on a largescale commercial basis has been a time consuming and expensive process.This was mainly because of the problem of effective disposal of aninsoluble or undigested solid or sludge component which was mainlyformed from animal faeces which was sometimes mixed with undigestedlivestock feed. Animal faeces contains proteins, protein breakdownproducts, fats, complex carbohydrates and lignocellulose. Lignocelluloseis an amorphous matrix of hemicellulose and lignin. Hemicelluloses arepolysaccharides which are usually branched and formed from sugars anduronic acids. Lignins are highly cross-linked aromatic polymers of noregular repeating unit because of their formation by free radicalcondensation. Lignocellulose in the animal faeces is derived from barley(e.g. barley awns), lucerne, sorghum and other stockfeeds.

Reference is made to Australian Patent Application 91080/91 (ie.International Patent Application PCT/AU91/00587 which was publishedunder WO 92/11210) which describes a waste treatment process and plantwhich comprises passing biological waste through one or more hangingcurtains made from two layers of a soft reticulated polyurethane foamand a reinforcing layer of synthetic material interposed therebetween.The curtains formed a support for filamentous micro-organisms whichformed a dense mat of cellular material. The micro organisms removedissolved phosphorus, nitrogen in the form of ammonia and carbon asorganic acids from the biological waste.

The process of Specification WO 92/11210 was extremely efficient inprocessing biological waste from distilleries and breweries as well asglycerol waste because this waste did not require an initial anaerobicfermentation step which is necessary in relation to waste from livestockfeedlots as described above. As stated in Specification WO 92/11210non-fermented biological waste must be subjected to an anaerobicfermentation step so as to break down complex macromolecules such ascarbohydrates, proteins, lipids to organic acids of 8 carbon atoms orless. This fermentation step takes place usually in the presence ofacidogenic fermentative bacteria which may produce organic acids such asvolatile fatty acids which may be readily metabolised to carbon dioxideby the hanging curtain technology described above.

After the fermentation period was completed which usually took 5 days ormore soluble digestible matter was collected as supernatant andseparated from the insoluble or undigested sludge component discussedabove which contained lignocellulose.

The conventional methods for disposal of the indigestible materialincluded passing the indigestible material to anaerobic ponds, septictanks or pits. Alternatively the indigestible material was dewatered byfiltration or by drying on open or covered sand beds. The dried sludgewas subsequently incinerated or used as fertiliser. In some cases theindigestible material was used as landfill.

However it will be appreciated from the foregoing that the presence ofthe indigestible material in the anaerobic fermentation tank or digestermeant that fermentation had to be stopped at periodic intervals of timeto remove the indigestible material which was time consuming, wastefuland expensive.

The indigestible material also could not be spread onto anaerobic pondsor used as landfill in Moslem countries such as Malaysia or Indonesia.In countries where this method of disposal could be achieved, it wasrelatively expensive because of the transportation costs.

The presence of the indigestible material in the anaerobic digester alsowas undesirable in that it accumulated in the digester over a period oftime and inhibited the fermentation reaction proceeding in an efficientmanner because of the production of phenolic compounds. These compoundswere also toxic to the filamentous micro-organisms used in the hangingcurtain technology of Specification WO/9211210.

It will also be appreciated that the indigestible material alsocontained many pathogenic microorganisms after the anaerobicfermentation step which were not eradicated prior to the pumping of theindigestible material as a slurry into anaerobic ponds or when spreadonto land and thus caused disease or infection. To avoid thispossibility it was necessary, as discussed in Henry et al Journal ApplBact. 55 89-95 (1983), to reduce the pH of the indigestible material topH 4.5 or lower (ie. below the pKa of the volatile fatty acids). In thisregard it will be appreciated that free volatile fatty acids caneliminate bacterial pathogens.

SUMMARY OF THE INVENTION

It therefore is an object of the invention to provide a process andplant for waste treatment which may alleviate at least to a certainextent the problems described above in regard to efficient disposal ofthe insoluble or undigested sludge component containing lignocellulose.

The process of the invention includes the following steps:

(i) passing waste material comprising an insoluble component through abioreactor system including a plurality of bioreactors in series andmaintaining said insoluble component as a suspension in said wastematerial;

(ii) passing treated waste material from said bioreactor system to oneor more acidification tanks to reduce the pH below 4.5 to produce freevolatile fatty acids for elimination of bacterial pathogens in saidtreated waste material; and

(iii) separating the insoluble component from the waste material beforeor after step (ii).

There is also provided a waste treatment plant including:

(i) a bioreactor system including a plurality of bioreactors in seriesfor treatment of waste material;

(ii) one or more acidification tanks to reduce the pH below 4.5 toproduce free volatile fatty acids for elimination of bacterial pathogensin said treated waste material; and

(iii) means for separating an insoluble component from said wastematerial after passage through the bioreactor system.

The waste material which is subject to the process of the inventionsuitably includes human or animal faeces and preferably faeces fromlivestock feedlots as described above which may have a stockfeedcomponent containing lignocellulose.

Each bioreactor may be interconnected by an overflow conduit so thatwaste material or influent i s quickly and efficiently transferred fromone bioreactor to an adjacent bioreactor without the need for pumpingmaterial so as to transfer material from one bioreactor to another.

Each bioreactor is suitably provided with agitation means which keepsthe contents of each bioreactor in the form of a slurry or suspension sothat the solid particles are maintained in the suspended state toachieve the object of the invention.

The contents of each bioreactor are also suitably subject to appropriateheating means and in one form this may be provided by steam being passedinto and out of each bioreactor. However, other forms of heating meansmay be utilised such as electrical heating. Preferably the temperaturein each bioreactor is maintained at a desired temperature by suitablythermostatically controlled means between 25°-50° C. and more suitably30°-40° C. In a preferred form the temperature is slowly decreased asthe waste material passes through each bioreactor from initially 40° C.to finally 30° C.

Preferably the pH of the waste material fed into the bioreactors ismaintained between 5.0-7.0 and more suitably between 5.8-6.4. Theretention time in each bioreactor may be 12-48 but more suitably 24hours.

After the waste effluent leaves the bioreactor system it may be passedthrough a filter or sieve to filter out the insoluble material which ispreferably incinerated or if it is to be spread onto land it may bepassed through acidification tanks as described hereinafter. It will beappreciated that removal of the insoluble material may take place in anysuitable manner. While filtration is a preferred procedure, flocculationmay also be utilised.

The supernatant or soluble liquid from the filter may then be passedinto the one or more acidification tanks and preferably maintained insaid tank(s) for a period of 24-48 hours to reduce the pH to a value ofbelow 4.5 and more suitably between 4.0-4.5 which is below the pKa ofthe volatile fatty acids e.g. acetic acid, propionic acid, butyric acid,valetic acid, caproic acid, enanthic acid as well as octanoic acid aswell as relevant isomers. Such volatile fatty acids (VFAs) are producedby the anaerobic bioreactor system and the lowering of the pH is toconvert VFA salts to free acid in the acidification tank(s). This willeliminate most, if not all bacterial pathogens.

In a variation of the above described procedure, in some cases the wasteeffluent after it leaves the bioreactor system may be passed through theacidification tank(s) before removal of the insoluble material. In thisembodiment after removal of the insoluble material the waste effluentmay then be passed to a curtain assembly as described hereinafter. Thisprocedure is preferable when it is impossible to incinerate theinsoluble material after filtration of the waste material after passageof the waste material through the bioreactor system.

There also may be provided means for maintaining an atmosphere of carbondioxide or other gas in said acidification tank(s) to inhibit the growthof yeasts in said acidification tank(s). Such means may, for example,comprise conduit(s) for the carbon dioxide or other gas which extendinto the or each acidification tank. Such conduits may be connected to asuitable source of carbon dioxide or said other gas.

Preferably in this embodiment there is provided means such asappropriate transfer conduits for transferring effluent gases (which mayinclude carbon dioxide) generated in the bioreactor system to theacidification tank(s) to maintain a gaseous atmosphere above the wastematerial being acidified. This feature as stated above is useful in thatit inhibits the growth of yeasts or fungi in the acidification tank(s)such as Candida ingens. The gases may subsequently be removed from theacidification tank(s) by appropriate conduit(s) to gas scrubbers foreventual discharge.

Preferably the waste material is subjected to a further treatment stepto remove nitrogen in the form of ammonia, dissolved phosphorous andcarbon in volatile fatty acids. More preferably a suitable means forremoving nitrogen in the form of ammonia, dissolved phosphorous andcarbon is a hanging curtain assembly. In this particular embodiment, thewaste from the acidification tank(s) may be passed to a hanging curtainassembly, which maybe, for example, a hanging curtain assembly of the ofthe type described in Patent Specification 91080/91. Some of the carbonis evolved as carbon dioxide with the remainder being retained by themicro-organisms contained therein in the hanging curtain assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference may now be made to a preferred embodiment of the invention asshown in the attached drawings wherein:

FIG. 1 is a flow diagram of a waste treatment plant constructed inaccordance with the invention;

FIG. 2 is a flow diagram of an alternative form of waste treatment plantconstructed in accordance with the invention.

DETAILED DESCRIPTION

In FIG. 1 there is shown an in-ground holding tank 10 for influentcomprising faeces admixed with undigested feed or waste feed from apiggery (not shown). The influent is pumped by a feed pump 11 through amacerator 12 which grinds the particles in the influent into smallpieces or finely divided material before the influent is passed intobioreactor 13 provided with agitator 14 having shaft 15 mounted inbearing 16. There is also provided conduit between holding tank 10 andmacerator 12, conduit 18 between feed pump 11 and macerator 12 andconduit 19 which provides communication between inlet conduit 20 andbioreactor 13. Conduit 20 is provided with a shut off valve V₁ and flowcontrol diaphragm valve V₂. Conduit 21 functions as a return line forrecycling influent from bioreactor 13 through conduit 20 back to holdingtank 10 which depends upon operation of valves V₁ and V₂.

There is also provided additional bioreactors 13A, 23B, 13C, 13D and 13Eall having a similar construction to bioreactor 13. There is providedoverflow conduits 22 between adjacent bioreactors for transfer of fluid.Each bioreactor is also provided with a drain line 23 having a shut offvalve V₁.

There is also provided a steam boiler 24 into which raw water is fedthrough conduit 25 also provided with a single valve V₁. Steam may thenpass into conduit 26 having a pressure control valve assembly 27.

There is also provided a plurality of steam conduits 28 which eachcommunicate with supply conduit 26 as shown which pass steam into eachof the bioreactors 13-13E as shown. Each steam conduit 28 is alsoprovided with a vacuum breaker valve V₃ to stop back siphonage of fluidas shown. There is also provided a shut off valve V₁ in each conduit 28as well as a further valve V₁ associated with a temperature controlvalve 29 in the form of a sliding gate valve associated with conduit 30which also has a thermostat or thermostat controller 31 in the form of aprobe which extends into each bioreactor which controls the temperatureattained in each bioreactor 13-13E.

There is also provided an outlet conduit 32 with each bioreactor 13-13Ewhich each communicates with conduit 33 for passing effluent gases totanks 48, 50 and 56 described hereinafter via transfer conduit 32A andinlet conduits 33A, 33B, and 33C. Effluent gases may then pass through areturn line 34A from gas line 49A to a pair of gas scrubbers 34connected in parallel as shown. The bottom gas scrubber 34 has anassociated conduit 35 and the top gas scrubber 34 has an associatedconduit 36. Each of conduits 35 and 36 are shut off with valves V₄ andcommunicate with conduit 37 which communicates with fan 38 and stack 39.There is also provided steam trap 40. Valves V₄ function to take one ofscrubbers 34 out of service for maintenance purposes.

The effluent after it passes out through the final bioreactor 13E ispassed through a feed pump 41 through conduit 42 and subsequentlythrough conduit 43 to a sludge filter 44. Pressure indicators 51 areshown associated with conduit 43 as well as conduit 47. A solid fraction45 from sludge filter 44 is retained in container 46 whereby solidfraction 45 which is mainly lignocellulose may be transferred by truck46A for incineration or other form of disposal. A liquid fraction richin volatile fatty acids or VFAs is then passed to a VFA feed tank 48through conduit 47 where it is held for 2 days before being passedthrough conduit 52 to a transfer pump 53 before being fed into VFAholding tank 50 via conduit 54 which communicates with conduit 55.

Conduit 28A functions to transfer steam from conduit 26 to a VFA liquidacidification tank 56 which is fed with sulfuric acid (H₂ SO₄) from asulfuric acid feed tank 57 which is associated with an inlet conduit 58having a pressure relief valve V₅ and a drain conduit 59 whichcommunicates with conduit 62 which passes through a sulfuric acid pump60. There is also provided a sump 61. The sulfuric acid is passedthrough conduit 62 which communicates with conduits 58 and 59 as shownto acidification tank 56 which is also provided with an agitator 14 asshown. Each of agitators 14 and associated shafts 15 in bioreactors13--13E as well as tank 56 are provided with a variable speed control(VS) shown in phantom. Material may be passed from tank 56 to conduit 52through conduit 49 which thereafter may be transferred to conduit 55 andhence to tank 50 or alternatively to tank 56 though conduit 57 dependingupon operation of shut off valves V₁.

There is also provided conduits 64, 63 and 65 which each communicatewith tanks 48, 56 and 50 respectively for transferring effluent gasesback into gas line 49A and subsequent flow through return line 34A.Conduit 67 is also shown having temperature controller 31 for control oftemperature in tank 56. Conduit 67 communicates with conduit 28A asshown via temperature control valve 29.

Tank 50 is also provided with temperature indicator 68 and tank 56 isalso provided with pH indicator 69 as shown.

Liquid from VFA holding tank 50 is passed to a hanging curtain assembly70 through conduit 71 and passed through a curtain feed pump 72 providedwith a variable speed control VS. Conduit 71 may be split into separateconduits 73 and 74, 75 and 76 as well as 77 and 78 which may applyliquid waste as shown to either side of a curtain module or curtainsubassembly 79A. There also may be utilised three additionalsub-assemblies 79B if required to increase the waste treatment capacityof hanging curtain assembly 70. The flow connections of sub-assemblies79B to pump 72 are omitted for clarity. Each of sub-assemblies 79A and79B are retained in a housing 80 having a sloping drain floor 81. Thereis also utilised a temperature indicator 82 which is associated withhousing 80.

Gases from housing 80 may be passed through conduit 83 through dampervalve V₆, cooling fan 84, and stack 85. There is also shown a furtherdamper V₆ which communicates with the interior of housing 80 and theoperation of each damper valve V₀ controls air flow through housing 80.Preferably the air pressure inside housing 80 is maintained less thanatmospheric.

Waste effluent may be passed from the sloping floor 81 of housing 80 toa treated waste holding tank 86 having a discharge pump 87 associatedtherewith via conduit 86A. There is also provided a level element 91which may control pump 87 for maintaining the level of fluid in housing80. There is also provided pH indicator 89. Fluid may be pumped by pump87 through discharge conduit 88 which has a return line 89A. Waste maybe recycled through conduit 90 to housing 80 as shown from conduit 88.Thereafter waste may be passed to a treatment pond 92 which communicateswith another pond 93 via conduit 94 with the assistance of pump 95.Waste may subsequently be transferred to a feed tank 96 via conduit 97.Thereafter conduit 97A may pass fluid to a treatment channel or flume 98of a piggery. Subsequently fluid may be passed to holding tank 10 via abypass plate 99 or alternatively through a conduit 100 to an in groundholding tank 101 having a discharge pump 102 which may transfer fluid totreatment pond 92 through conduit 103.

In an alternative arrangement as shown in phantom material from conduit88 may be transferred through conduit 104 to a filter 105 whereby asolid fraction 107 may be deposited in container 106 before beingremoved by truck 108A for incineration or other form of disposal. Aliquid fraction may be passed from filter 105 via conduit 105A to aliquid tank whereby it may be recycled to flume 98 via conduit 109 andwith the assistance of pump 110.

FIG. 2 represents a modified waste treatment plant in contrast to thewaste treatment plant shown in FIG. 1. Similar reference numerals areutilised for the sake of convenience. One difference between the FIGplant and the FIG. 2 plant is the adoption of bioreactors 13-13F on aslope as indicated with overflow conduits 22 facilitating transfer offluid from adjacent bioreactors. Valves are also not indicated for thesake of convenience. One conduit 18 interconnects holding tank 10 andbioreactor 13 and steam from boiler 24 flows through conduit 26 andsubsequently through inlet conduits 28 to a respective bioreactor13-13F. Exhaust conduits 32 for gas also communicate with main transferconduit 33 as described above in the FIG. 1 waste treatment plant.

Gas is passed to acidification tanks 56A and 56B through conduit 33 andinto each tank through inlet conduits 33A and 33B as shown. There isalso supplied a gas return line 34A to gas scrubbers 34.

In a variation of the procedure shown in FIG. 1, the waste effluent orwaste material after emerging from the final bioreactor 13F may betransferred directly to acidification tank 56A through conduit 44A shownin phantom. In this variation the waste material will still have theinsoluble component entrained therein so that the waste material maythen be transferred from acidification tank 56B to filter 44 afterpassage through conduit 45A also shown in phantom. Subsequently, afterfiltration the liquid fraction may then be transferred to curtainassembly 70 through conduit 46A also shown in phantom.

Another difference is the adoption of two VFA liquor acidification tanks56A and 56B whereby a liquid fraction from sludge filter 44 is passedthrough conduit 47 and subsequently into tank 56A. Sulphuric acid ispumped by pump 60 from a tank or drum 57 via conduit 62 to tank 56A.Material may then be passed from tank 56A to tank 56B through conduit62A. Acid treated fluid may then be passed to curtain assembly 70through conduit 71.

Waste liquid after passing through curtain assembly 70 is passed tofilter feed tank 86 through conduit 86A whereafter fluid is pumped bypump 87 to treatment pond 92 by conduit 88 or passed through recyclingconduit 90 to curtain assembly 70 after passage through conduit 104A.Liquid from pond 92 is passed through conduit 97 back to flume 98 withthe agency of pump 95. Fluid may also be passed to filter 105 fromcurtain assembly 70 through conduit 104A whereby a liquid fraction maybe passed to treatment tank 108 through conduit 105A whereafter fluidmay be passed to conduit 97 through conduit 109 assisted by pump 110.

The waste being passed through the series of bioreactors is seriallydigested by a different population of flora in each tank. The short meanresidue time in each tank (˜24 hours) permits a specific flora todevelop in each tank and progressively digest the material beingpassaged. The end result is the product of volatile fatty acids (VFAs)i.e. C₂ -C₈ (acetic, propionic, butyric, valeric, caproic, heptanoic andoctanoic acids and relevant isomers). Non-volatiles such as lacticand/or succinic acids are not produced. Traces (˜-3 mML⁻¹) ofphenylacetic acid do appear. The purpose of restricting the end productsof fermentation to VFAs ensures an excess of these acids is present toeffect destruction of bacterial pathogens present in the waste.

The serial fermentation also enables conditions of pH, fermentation andresidue time in each bioreactor to be manipulated in order to optimiseproduction of the VFAs.

    ______________________________________                                        WASTE TREATMENT PLANT                                                         DESIGN CRITERIA                                                               ______________________________________                                        1.0 GENERAL                                                                       Atmospheric Pressure   101.325 kPa                                            Min Design Temperature 15° C., 50% relative                                                   humidity                                               Max Design Temperature 32° C., 100% relative                                                  humidity                                               Operating Schedule     7 days/week, 24                                                               hours/day                                          2.  FEED DEFINITION                                                               Feed Material          Piggery flume floor                                                           flushings                                              Treatment Capacity     1500 L/day                                             Feed % Solids          3% w/v                                                 Solids Size Range      2-5 mm                                                 Feed pH                5.8-6.4                                                Design Temperature - Min                                                                             20° C.                                          Design Temperature - Max                                                                             30° C.                                          Design Availability    85%                                                    Design Flow            73.5 L/h                                           3.0 FEED TANK                                                                     Type                   Inground                                               Material               Concrete                                               Retention Time         24 hours                                               Capacity               1500 L nominal                                         Temperature            20° C.-30° C.                        4.0 ANAEROBIC BIOREACTORS                                                         No. Stages             6                                                      Retention Time per stage                                                                             24 hours                                               Temperature Reaction   1 40° C.                                                               2 35° C.                                                               3 35° C.                                                               4 35° C.                                                               5 30° C.                                                               6 30° C.                                        % of solids fermented  45%                                                    Tank material          FRP (Isophthalic)                                      Agitation              Suspension (0.25                                                              kW/m.sup.3 approx)                                                            S.S. 316 A310                                                                 impeller                                           5.0 FERMENTATION PRODUCT                                                          pH                     5.8-6.4                                                Temperature            30° C.                                          % Solids               1.5% w/v                                               Solids Composition     Lignocellulose                                     6.0 POST FERMENTATION FILTRATION                                                  Filtration Rate        L/m.sup.2  · h                                Filter Cake Moisture   % moisture wet                                                                basis                                                  Product Calorific Value                                                                              20 MJ/kg, air-dry                                      Kg Product per Day     25                                                 7.0 ACIDIFICATION                                                                 Retention Time (batch) 48 hours                                               No. Tanks              3 (series batch)                                       pH after Acidification 4.5                                                    Acid Addition Rate     2-3 mL H.sub.2 SO.sub.4 per L                                                 filtrate                                               Temperature            Natural                                                Acid Consumption       3-4.5 L/day                                            Acid Storage           200 L drums                                            Acid Delivery          Via drum pump or                                                              manual                                                                        container                                                                     addition                                           8.0 FEED TO CURTAINS                                                              Analysis                                                                  Acetic Acid 137 mmol/L     0.82% w/V                                          Propionic Acid                                                                            37 mmol/L      0.27% w/v                                          Butyric Acid                                                                              38 mmol/L      0.33% W/V                                          Valeric Acid                                                                              10 mmol/L      0.10% w/v                                          Caproic Acid                                                                              3.1 mmol/L     0.04% w/v                                              Total Volatile Fatty Acids                                                                           1.57% w/v                                              Feed rate - average    62.5 L/h                                           design                                                                            73.5 L/h                                                                      pH                     4.5                                                    Temperature            30° C.                                      9.0 CURTAIN MODULE                                                                Curtain Treatment Capacity                                                                           40-100 L/m.sup.2 day                                   No. Curtains           3                                                      Curtain Fall           3 m or greater                                         Operating Temperature - Max                                                                          37° C.                                          Air Temp in            28° C.-32°                               % Relative Humidity    90%                                                    % Relative Humidity    100%                                                   Distance between curtains                                                                            150 mm                                             ______________________________________                                    

I claim:
 1. A waste treatment process including the steps of:(i) passingwaste material comprising an insoluble component through a bioreactorsystem including a plurality of bioreactors in series and maintainingsaid insoluble component as a suspension in said waste material; (ii)passing treated waste material from said bioreactor system to one ormore acidification tanks to reduce the pH below 4.5 to produce freevolatile fatty acids for elimination of bacterial pathogens in saidtreated waste material; and (iii) separating the insoluble componentfrom the waste material before or after step (ii).
 2. A process asclaimed in claim 1 including a further step of treating waste materialto remove nitrogen in the form of ammonia, dissolved phosphorous andcarbon as volatile fatty acids.
 3. A waste treatment process as claimedin claim 1 wherein said waste material is agitated each bioreactor sothat said waste material is maintained in the form of a slurry orsuspension to maintain said insoluble component in a suspended state. 4.A waste treatment process as claimed in claim 1 wherein said wastematerial in each bioreactor is heated to a temperature of between 25°1450° C.
 5. A waste treatment process as claimed in claim 4 wherein thetemperature is maintained between 30°-40° C.
 6. A waste treatmentprocess as claimed in claim 5 wherein the waste material is initially ata temperature of 40° C. in said bioreactor system before the temperatureis slowly decreased to 30° C.
 7. A waste treatment process as claimed inclaim 1 wherein the pH in said bioreactor system is maintained between5.0-7.0.
 8. A waste treatment process as claimed in claim 7 wherein thepH is maintained between 5.8-6.4.
 9. A waste treatment process asclaimed in claim 1 wherein said waste material is maintained in eachbioreactor for 12-48 hours.
 10. A waste treatment process as claimed inclaim 9 wherein said waste material is maintained in each bioreactor for24 hours.
 11. A waste treatment process as claimed in claim 1 whereinthe waste material after leaving the bioreactor system is passed througha filter or sieve to filter out the insoluble component.
 12. A wastetreatment process as claimed in claim 11 wherein a liquid fractionremaining after removal of the insoluble component is passed into saidone or more acidification tanks for a period of 24-48 hours.
 13. A wastetreatment process as claimed in claim 2 wherein said waste materialafter passage through said one or more acidification tanks is passedthrough a hanging curtain assembly for removal of said nitrogen in theform of ammonia, dissolved phosphorous and carbon as volatile fattyacids.
 14. A waste treatment process as claimed in claim 1 wherein thepH is reduced to a value of between 4.0-4.5.
 15. A waste treatmentprocess as claimed in claim 1 wherein an atmosphere of carbon dioxide oreffluent gases is maintained in the or each acidification tank toinhibit growth of bacterial pathogens.
 16. A waste treatment plantincluding:(i) a bioreactor system including a plurality of bioreactorsin series for treatment of waste material; (ii) one or moreacidification tanks to reduce the pH below 4.5 to produce free volatilefatty acids for elimination of bacterial pathogens in said treated wastematerial; and (iii) means for separating an insoluble component fromsaid waste material after passage through the bioreactor system.
 17. Awaste treatment plant as claimed in claim 16 wherein each bioreactor isconnected to an adjacent bioreactor by transfer conduit.
 18. A wastetreatment plant as claimed in claim 16 wherein each of said bioreactorsare supported on a slope with an initial bioreactor located on a moreelevated position than a final bioreactor.
 19. A waste treatment plantas claimed in claim 16 wherein there is provided heating means in eachbioreactor to maintain an operational temperature of between 30°-40°.20. A waste treatment plant as claimed in claim 19 wherein said heatingmeans includes means for injection of steam into each bioreactor.
 21. Awaste treatment plant as claimed in claim 20 wherein there is provided asteam boiler connected to a steam conduit which is connected toinjection conduits which communicate with each bioreactor.
 22. A wastetreatment plant as claimed in claim 19 wherein there is providedthermostatically controlled means to maintain said operationaltemperature in each bioreactor.
 23. A waste treatment plant as claimedin claim 16 wherein each bioreactor is provided with agitation means tomaintain said waste treatment material in a suspended state.
 24. A wastetreatment plant as claimed in claim 16 wherein said separating meansincludes a filter or sieve to separate said insoluble component from aliquid fraction of said waste material.
 25. A waste treatment plant asclaimed in claim 16 wherein there is provided means to maintain anatmosphere of carbon dioxide or other gas in said acidification tank(s)to inhibit growth of yeasts.
 26. A waste treatment plant as claimed inclaim 25 wherein said means to maintain an atmosphere of carbon dioxideincludes transfer means to transfer effluent gases generated in saidbioreactor system to said acidification tank(s).
 27. A waste treatmentplant as claimed in claim 26 wherein said gases from said acidificationtank(s) are transferred to gas scrubbers for discharge.
 28. A wastetreatment plant as claimed in claim 16 wherein there is further provideda treatment means in communication with said one or more acidificationtanks to remove nitrogen in the form of ammonia, dissolved phosphorousand carbon as volatile fatty acids from said waste material.
 29. A wastetreatment plant as claimed in claim 28 wherein said treatment meansincludes a hanging curtain assembly.